In contrast, a transaction that is revenue in nature deals with short-term items - i.e income and expenses.

Here are the answers:

Capital. Land is a non-current (long-term) asset.

Capital. installation costs form part of an asset's cost. Since assets are long-term, so are installation costs.

Same as b). Erection costs form part of the cost of the machinery (or other asset).

Revenue nature. Commission and other employee costs (salaries and wages) are expenses.

Revenue. Repairs and maintenance are expenses. (In contrast, improvements are capital as they result in an asset with higher value. Repairs and maintenance maintain an asset's value - they do not improve it - so these are counted as expenses.)